1. Field of the Invention
This invention pertains to a method and apparatus for performing a coronary artery bypass procedure. More particularly, the present invention reverses flow in a portion of a coronary artery and a coronary vein to direct flow from an oxygenated chamber of the heart through the vein in a direction opposite normal flow and from the myocardium through the artery in a direction opposite normal flow and into a reduced pressure chamber of the heart.
2. Description of the Prior Art
Coronary artery disease is the leading cause of premature death in industrialized societies. Numerous techniques have been developed for bypassing an obstructed or diseased coronary artery. Angioplasty attempts to expand an occluded site. Commonly, a balloon-equipped catheter is used to expand an occluded site. A stent may be placed at the expanded site for the purpose of preventing reblockage. Coronary artery bypass grafting uses a harvested blood vessel from the patient to graft a bypass from the aorta to the occluded artery. Such prior art procedures have numerous problems including restenosis of angioplasty treated vessels. Grafting techniques are highly traumatic and present other problems.
New methods have been proposed as alternatives to traditional angioplasty and bypass grafting. These methods include providing a direct blood flow path from the left ventricle directly through the heart wall to the coronary artery and are described in U.S. Pat. Nos. 5,429,144, dated Jul. 4, 1995; 5,287,861, dated Feb. 2, 1994; and 5,409,019, dated Apr. 25, 1995 (all to Wilk). All of these techniques include providing a stent in the heart wall to define a direct flow path from the left ventricle of the heart to the coronary artery. The stent is closed during either diastole or systole to block return flow of blood from the coronary artery during the heart's cycle. For example, the '861 patent teaches a stent which collapses to a closed state in response to heart muscle contraction during systole. The '019 patent (particularly FIGS. 7A and 7B) teaches a rigid stent (i.e., open during systole) with a one-way valve which closes during diastole to block return flow of blood from the coronary artery. Such techniques for interruption of blood flow during either diastole or systole are undesirable since such interruption can result in areas of stagnant or turbulent blood flow. Such areas of stagnation can result in clot formation which can result in occlusion or thrombi breaking loose. Providing direct blood flow from the left ventricle to the coronary artery has been criticized. For example, Munro et al, "The Possibility Of Myocardial Revascularization By Creation of a Left Ventricle Coronary Artery Fistula", 58 Journal Thoracic and Cardiovascular Surgery, pgs. 25-32 (1969) shows such a flow path in FIG. 1. Noting a fallen coronary artery flow and other adverse consequences, the authors concluded "that operations designed to revascularize the myocardium direct from the cavity of the left ventricle make the myocardium ischemic and are unlikely to succeed." id at pg. 31.
In addition to the foregoing, techniques have been developed to directly revascularize the myocardium. For example, U.S. Pat. No. 5,429,144 to Wilk (FIGS. 10-12) teaches passing a stent from either the coronary artery or the left ventricle directly into but not through the myocardium for direct revascularization of the myocardium. However, these techniques are unsuitable. For example, Roque Pifarre, M.D. et al, in "Myocardial Revascularization From the Left Ventricle: a Physiological Impossibility", 19 Surgical Forum, 157-159 (1968), concluded that blood flow from the ventricular lumen to the myocardium to artificially create channels is a physiologic impossibility due to pressure differentials. Also, supplying a flow of blood to the myocardium without adequate drainage of blood from the myocardium can result in heart swelling and edema.